Now, a small, preliminary Brazilian study finds that most women who have the procedure are satisfied with their new look.

Experts caution, however, that some buttocks-enhancement procedures -- especially when performed by unqualified people -- come with real risks.

The study technique involved liposuctioning excess fat where it's not wanted -- such as from the hips and thighs -- and injecting, or grafting, it into the buttocks to plump them up.

A good result "does not depend on a lot of fat infiltration," said study leader Dr. Rodrigo Rosique, a plastic surgeon in Goiania, Brazil, but rather on the skilled method of combining the liposuction and the injections. Avoiding large injections of fat into any one area of the buttocks is key, he said.

"The degree of satisfaction is amazing, and it is overwhelming how the fat grafts [injections] really take into the patients' buttocks," said Rosique, a professor of plastic surgery at Federal University of Goias.

Rosique followed up on 58 women, aged 19 to 62, who had the procedure done between 2010 and 2012. All but one patient reported feeling very satisfied. The other patient had additional surgery six months after her first one and then reported being satisfied with the result.

Women whose weight changed by more than 10 percent after the procedure were excluded from the follow-up evaluation.

"I took these patients out because the buttocks' final volume could be affected by the weight change, misunderstanding if the volume enhancement was due to weight gain or the graft," he explained.

Rosique is scheduled to present the findings Sunday at the annual meeting of the American Society of Plastic Surgeons, in San Diego. The research should be viewed as preliminary until published in a peer-reviewed journal.

None of the study patients reported medical complications. Five patients had a pocket of clear fluid that collected at the fat-removal site, which was treated by draining it.

"The sculpting can give a very pleasing result," said Dr. David Reath, a Knoxville, Tenn., plastic surgeon who chairs the society's public education committee. He was not involved in the Brazilian study.

The procedure takes about two and a half to three hours, Rosique said. Patients can return to work in about a week.

The researchers said avoiding the injection of large volumes of fat in any particular site avoids the problems of tissue death. The Brazilian researchers used an epidural anesthesia. In the United States, Reath said, an epidural or a general anesthesia typically would be used.

In the United States, plastic surgeons performed more than 3,700 buttocks procedures in 2012, including lifts and implants, according to the society. The average surgeon fee for the procedures is about $4,600.

Reath said, however, that patients should check carefully to see if their doctors are qualified. Recently, a number of deaths have been reported in the United States among women who have gone to so-called "pumping parties," at which nonmedical-grade silicone is sometimes used to plump up the buttocks and fill out facial lines.

Unqualified persons inject the type of liquid silicone bought at hardware stores. The fat solvent in the silicone can cause severe problems, such as traveling to the lungs and obstructing the airways.

"People can be disfigured or have worse complications," Reath said.

Deaths from illegal buttocks injections have been reported in Alabama, Georgia, Florida, Pennsylvania, Nevada and New York. In another case, a woman who reportedly went to a pumping party arrived at an emergency room coughing up blood. Doctors found clots in the small blood vessels in her lungs and discovered that the injected silicone had traveled there and led to obstructions.